[sdiy] SVF: 2-pole to 4-pole ?

[Ray Wilson]

Hi Mark

All of the designs I have seen that make this claim actually involve 2 two
pole filters which are then able to be switched into a single 4 pole filter.
In most filter designs a pole involves a capacitor and a VC controlled
variable gain block.

Ray

-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of mark s
Sent: Monday, November 10, 2003 12:25 AM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] SVF: 2-pole to 4-pole ?


i am a little discouraged by the phase shifter thing...thank you for the
responses, will look into them to try and understand what dome filters, FIR
filters are. seems like the most straightforward solution would be to delay
the sampled (digit at l) circuit.

another, probably easier, question.

although don lancaster refers to it in the active filter cookbook, i can
not see how to transform a 2-pole state-variable filter (freq, Q and gain
being tunable) into 4-pole. (i would like to do it with a
switch.)  .....something about changing the 'a' factor (gain) but i don't
get it. hints would be appreciated.

thanks
mark